Effect of shading on the physiological and reproductive parameters in Nelore cows.

This study aimed to evaluate the physiological and reproductive parameters of Nelore cows under various microclimatic conditions. The experiment was performed in Central Brazil, which has a tropical climate with dry winters and rainy summers. The experimental groups were divided into an area with shading (5.8 trees/ha; n = 42) and an area with little shading (0.4 trees/ha; n = 42). The physiological (heart rate, respiratory rate, rectal temperature, surface body temperature, and vaginal temperature) and reproductive (estrus detection, conception rate, and rate of pregnancy loss) parameters were then assessed. The rectal temperature (p = 0.002); surface body temperature on the flanks, forehead, and shoulder (p < 0.001); and vaginal temperature (p < 0.001) of cows in the group with shading were significantly lower than those of cows in the group without shading. Estrus was higher (p = 0.08) in the shaded group; however, no effect was observed on conception and pregnancy loss rates. In conclusion, shading (5.8 trees/ha) provided better thermal comfort for Nelore animals in the tropical climatic region. However, this did not affect their performance after fixed-time artificial insemination.

Influence of long-term thermal stress on the in vitro maturation on embryo development and Heat Shock Protein abundance in zebu cattle.

The objective of this study was to investigate the influence of long-term temperature stress during the in vitro maturation (IVM) of oocytes on the in vitro embryo production (IVP) and the abundance of HSP70 and HSP90 in zebu cattle. Viable cumulus-oocyte complexes (COCs) were incubated for 24 h at 37 °C, 38.5 °C, or 40 °C for the low-, physiological, and high-temperature stress treatments, respectively. Thereafter, they were subjected to in vitro fertilization and culture. Temperature did not affect the polar body extrusion. However, IVP was adversely affected when IVM took place at 37 °C and 40 °C. The highest abundance of HSP70 was observed in cumulus cells after maturation of COCs at 40 °C. In contrast, HSP70 was more abundant in oocytes at both 37 °C and 40 °C; however, at 40 °C, the difference to the control group (38.5 °C) was not significant. In contrast, the highest abundance of HSP90 was observed in oocytes and cumulus cells at 37 °C. It appears that HSP70 and HSP90 respond to cold and heat stress in different ways. In conclusion, moderately high (40 °C) and low (37 °C) thermal stress for 24 h during IVM is detrimental to the developmental competence of oocyte and is accompanied by changes in the abundances of HSP70 and HSP90, especially in cumulus cells.

Anti-Müllerian hormone (AMH) as a predictor of antral follicle population in heifers.

Antral follicular population (AFP) and anti-Müllerian hormone (AMH) concentration are strongly associated. Thus, analyzing AMH concentration is a reliable method to predict animals with high AFP, an important feature to select donor cows for embryos and oocytes. However, not much is known about this parameter in heifers, particularly in crossbred animals. The aim of this study was to assess AFP in heifers and cows and its relation to serum AMH levels. Bos taurus indicus cows (36-60-months-old; n = 30) and heifers (12-14-months-old; n = 17) of the same breed were evaluated. A single procedure of follicular counting was performed by ultrasound for each animal. Random sampling was performed to analyze serum AMH concentration. Cows showed higher AFP than heifers; nonetheless, plasma AMH concentration did not differ between the categories. A high correlation of AFP with plasma AMH concentration was observed in Girolando heifers. Thus, it is suggested that AMH concentration could be a reliable and less invasive method for selecting heifers with high AFP.